Lascar DPM 160 Application Notes Download Page 1 | Manualshive

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ICl

7660

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10

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10

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0V

1

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3

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AD595

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1M

10K

14

+5V -5V

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COM

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ICL 8069

ICL 8069

10

µ

2k2

Panel Instrument

Application Notes

Issue 3

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Summary of Contents for DPM 160

Page 1: ...4 5 3 0 V 1 4 1 3 7 1 1 8 9 3 1 2 A D 5 9 5 1 0 V 1 M 1 0 K 1 4 5 V 5 V V D D V V S S V I N H I I N L O C O M D P M R E F R E F L O 1 M 1 0 µ 1 0 K 2 0 K 1 0 K I C 8 0 6 I C L 8 0 6 9 1 0 µ 2 Panel Instrument Application Notes Issue 3 ...

Page 2: ... 7 Reducing Ground Loop Errors 7 Noise 8 4 Interfacing with Linear and Digital Circuitry 9 Linear 9 Digital Signals 10 5 Power Supplies 11 Negative Rail Generators 11 Operation from Low Volt Supplies 11 6 Fitting an External Reference 12 7 Parallel Operation 12 8 LCD Backlighting 12 9 Commissioning the Meter 13 Handling 13 Circuit Connection 13 Bezel Fitting 13 Using PCB Links 15 10 Troubleshootin...

Page 3: ...ion Put simply the technique involves charging a capacitor CINT from zero at a rate directly proportional to the input voltage and for a fixed time see fig 1 2 This is the integrate phase Then the control connects the reference voltage note that it is negative and CINT is discharged at a rate proportional to the reference voltage This is the reference integrate or de integrate phase the end of whi...

Page 4: ...M e v i r D t n e m g e S k P k P V 6 5 4 V 9 V o t V 8 3 1 X A M 6 3 1 X A M e v i r D e n a l p k c a B k P k P µ µ µ µ A m 5 2 5 1 V 3 e g a t l o v t n e m g e S V 0 5 V 4 B A t p e c x E t n e r r u C g n i k n i S t n e m g e S AB4 only 3 5 T I N U X A M P Y T N I M S N O I T I D N O C S R E T E M A R A P MAX 140 ONLY 1 2 Multiplication Division Most Lascar voltmeters have either 3 or 4 digi...

Page 5: ...3 2 3 n i P V 0 n i V t n e r r u c e g a k a e l t u p n I Scale factor temperature coefficient Vin 199 0mV 0 V 5 3 2 3 8 2 8 2 n i p o t V e g a t l o v N O M M O C A m 6 0 V 1 0 y b d e s i a r M O C e g a t l o v k n i s N O M M O C A 2 1 V 1 0 y b d e r e w o l M O C e g a t l o v e c r u o s N O M M O C V 8 5 3 5 5 4 V 9 V o t V 6 3 n i p o t V e g a t l o v D N G D A m 2 1 V 5 0 y b d e s i...

Page 6: ...egative than the positive supply This is selected to give a minimum end of life battery voltage of about 6V However COM can be used as a reference voltage When the total supply voltage is large enough to cause the zener to regulate 7V the Common voltage will have a low voltage coefficient 001 low output impedance 15W and a temperature coefficient typically less than 80ppm C Within the IC COM is ti...

Page 7: ...offsets but each reading results in a different current consumption If there is a change in current consumption there is a change in the reading which causes a change in current consumption etc A good example would be a DPM 40 reading say 1001 A drop of one count gives 1000 a difference of 4 segments in the least significant digit Each segment consumes 8mA Thus the total change in current is 4 x 8...

Page 8: ...beads can be very effective in reducing noise in signal lines 3 3 4 Stray Fields If stray electrical or magnetic fields are suspected of causing noise physical screening of the meter may be necessary Other measures include placing the meter away from cables that are likely to have large and noisy currents in them Another source of magnetic interference will be any transformer especially one operat...

Page 9: ...tion 3 Be careful not to exceed the maximum supply voltage the maximum supply voltage quoted in data sheets is the maximum voltage between V and V If the maximum supply voltage is 15V the maximum split supply is 7 5V If the battery is formed with separate cells it is as well to have a centre tap in the battery for the ground 0V However if you are using a packaged battery such as the PP3 then other...

Page 10: ... Where separate supplies are used ensure that they are commoned by joining the positive supplies together and that suitable level shifting networks are used see Fig 4 5 LCD digital signal level shifting Fig 4 4 Buffering Digital Ground V V V V DGND TEST DIGITAL GROUND V V V V V V V V DPM DPM IT 1700 100k 100k S S D D DGND 4 2 Digital Signals Where separate supplies are used ensure that they are co...

Page 11: ...ATIVE RAIL GENERATORS 5 2 OPERATION FROM LOW VOLT SUPPLIES Negative rail generator Single cell operation V V Add Current Limiting Resistor Clamping Diodes 5V 0V COM 10 F µ 10 F µ 2 4 8 3 5 7660 V IN HI IN LO V 5V VIN DPM 0V 10 F µ 10 F µ 10 F µ 10 F µ 2 2 4 4 8 8 3 3 5 5 7660 V IN HI IN LO COM V VIN DPM 6 6 7660 1 5V www lascarelectronics com 10 Installation Operation Section A 5 POWER SUPPLIES Th...

Page 12: ...h an isolated supply it is possible to destroy at least one meter With shunts in each of the 24V supplies there will be 48V between the meter IN LO inputs Fig 7 2 shows a better arrangement The general rule is don t use the same supply if you cannot use the same signal ground Ensure that when meters with internal references are parallel and COM is used as the ground e g in battery powered equipmen...

Page 13: ...ier post etc then ensure that the unit is well packed This is especially important in the case of LCD panel meters Keep bezel materials away from the glass and do not use such packaging as padded bags Firm cardboard boxes should be used Padded bags may protect against impact but not against crushing 9 2 Circuit Connection It is recommended that all connections to the meter be made with a socket Do...

Page 14: ...screws provided secure the two plastic spring clips to the rear of the meter The meter is designed to fit directly onto OKW Type M P and Veronex size 3 enclosures Installation Operation Section A Fig 9 6 900 Series modules Fig 9 7 Din Cased Series modules Locate the meter by passing it through the front panel cut out gently pushing until the rear of the bezel is flush with the panel The snap in lu...

Page 15: ...on trouble shooting DPMs Note Fig 9 10 V Series modules Fig 9 9 SP Series modules Slide the seal over the rear of the meter and fit round the meter rim Locate the meter by passing it through the front of the panel cut out and push until the rear of the bezel is flush with the panel Slide the fixing clip over the rear of the module and press firmly into place Fit the module to the bezel and slide t...

Page 16: ...N HI IN LO These resistors must be rated to withstand high voltages 2 MEASURING CURRENT Although measuring current simply means measuring the voltage across a low value resistor which has been placed in series with the current there are some potential pitfalls see Chapter 1 section 6 The thing to remember is to ensure that the signal to the meter is within its common mode range The commonest mista...

Page 17: ...D Current Monitoring Normal LCD Current Monitoring Fig 2 b Fig 2 c 220nF 470nF 5V SHUNT IN HI V IN LO COM V GND S TYPE DPM 10 F µ OUTPUT 78L05 7805 220nF 470nF 5V SHUNT IN HI V IN LO COM V DPM 10 F µ 10 F µ 10 F µ OUTPUT 0V 2 4 8 3 5 5V 7660 78L05 200 A F S µ 900Ω 90Ω 9Ω 0 9Ω 0 1Ω 2mA F S 200mA 20mA 2A DPM IN HI IN LO I IN I OUT Fig 2 d Multi range Current Measurement Always ensure IN LO is not co...

Page 18: ...ard L STANDARD L L STANDARD UNKNOWN Fig 3 1 Ratiometric Resistance Measurement VOLTAGE ACROSS STANDARD Vs VOLTAGE ACROSS UNKNOWN Vu V V REF HI REF LO IN HI IN LO COMMON RL RSTANDARD RUNKNOWN IL DPM 1 LCD 3 LED 3 LCD 4 DPM 340 DPM 160 DPM 125 DPM 390 DPM 300 DPM 1760 DPM 959 DPM 60 DPM 1763 DPM 2 DPM 200 S DPM 2000 S DPM 3 3 Measuring Resistance There are two basic methods of measuring the value of...

Page 19: ...995 or EMT 1900 However it is also possible to use a DPM with front end circuitry For S TYPE meters Fig 4 1 Fig 4 2 Using a Transistor as the Sensor For NON S TYPE meters Thermometer using the AD590 V V REF HI DPM REF LO IN HI IN LO COMMON 22kΩ 1MΩ 220kΩ 100kΩ 100kΩ 1MΩ 0 1 F µ TEMP SENSOR 0V 1k 4k3 15k 10µ 1k AD590 ICL 8069 9V PUSH TO READ 9V V IN LO REF LO IN HI COMMON REF TEST V DPM 0V 2k 15k 1...

Page 20: ... ratio of the applied voltage and is thus independent of supply voltage As with the resistance circuit ensure you choose a meter with separate input and reference connections and which can have the meter reference disconnected Arrange the ratio of R1 to R2 to give approximately 100mV across R2 Fig 5 Strain Gauge Application Some applications need the meter to have an offset eg tare The basic metho...

Page 21: ...use a DPM with front end circuitry Two basic techniques for AC DC conversion exist The simplest is the Precision Rectifier whose output is the average of the AC input Provided that the waveform of the input is constant the meter can be calibrated to read RMS values The second is the true RMS converter This can give the true RMS value of the input and is recommended for such applications as monitor...

Page 22: ...t LCD meters Measuring frequency is done by a frequency to voltage converter One advantage of the F V converter over the more conventional digital frequency meter is that it has a faster response to low frequencies Fig 8 a Fig 8 b Generating Overrange and Underrange Signals from LCD Meters Simple Two Range 4 Digit LCD Meter V V O R U R RANGE DGND DPM60 160 300 4001 V V U RANGE O RANGE AB BP E3 XG3...

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